The present invention relates to an anti-lock hydraulic brake system comprising a master brake cylinder, a pump unit, a supply reservoir and at least one wheel brake. The system further comprises a brake line between the master brake cylinder and the wheel brake into which an inlet valve is inserted. A relief line is provided between the supply reservoir and the wheel brake into which an outlet valve is inserted. A pressure line leading from the pump unit to the brake line with a separating valve in the brake line between the master brake cylinder and the point where the pressure line terminates into the brake line. The separating valve is switched into its closed position by the pump pressure. A regulating valve is provided for generating a pump pressure in the pressure line which is proportional to the pressure in the master brake cylinder.
Such brake systems have been described in the following publications: DE-OS No. 24 28 669, DE-OS No. 32 47 497, and DE-OS No. 24 28 669. These brake systems operate according to the following description: During a conventional braking operation, that is during braking without wheel slip control, the separating valves in the brake lines are open so that there is direct communication between the master brake cylinder and the wheel brakes. By depression of the brake pedal, the driver generates in the master brake cylinder a braking pressure which is supplied to the wheel brakes by way of the brake lines which are not closed, whereby the vehicle is slowed down. The rotational behavior of the wheels is constantly monitored so that an imminent locked condition of a wheel can be detected at once by a control circuitry. In order to prevent locking of the wheel, pressure fluid is discharged from the wheel brake and is replenished out of a pump for the purpose of renewed pressure build-up when the wheel has re-accelerated sufficiently. At the same time, the separating valves close so that the master brake cylinder is no longer connected to the wheel brakes. Since the master brake cylinder is then shut off hydraulically, the pedal cannot be displaced any further and therefore remains in the position it just adopted. The pressure in the master brake cylinder serves as a control pressure for a regulating valve which adjusts the pressure fluid supplied by the pumps to a pressure which is proportional to the pressure in the master cylinder and, respectively, proportional to the pedal force.
The embodiments in the cited published patent applications each show a disintegrated mode of construction of separating valve and regulating valve. This necessitates a considerable assembling effort when mounting the system into an automotive vehicle, since the individual components must be interconnected by pressure lines. This problem could be avoided if the separating valve and the regulating valve are incorporated in one common housing. However, this does not avoid the shortcoming that such a combined unit requires considerable mounting space. Therefore, the present invention has for its first object to devise a compact, space-saving assembly unit of separating valve and regulating valve.
Further, the systems described in the noted publications bear still another disadvantage. As has been explained above, pressure fluid is discharged out of the wheel brakes for regulating the wheel slip and is supplied into the wheel brakes after re-acceleration of the wheel. Depending upon how many control cycles per time unit are performed and how much pressure fluid was discharged, the pump must make available a specific volume of pressure fluid per time unit. The number of control cycles and the quantity of the discharged fluid depends on the friction conditions between the road surface and the tires. There is great volume requirement per time unit particularly when the transmissible forces between tires and road surface constantly vary. The consequence thereof is that when dimensioning the fluid output of the pump, one has to provide for this particular case. Therefore, the pump unit and hence the entire brake system become more costly.
Thus, it is another object of the present invention to provide means permitting the pump rate of delivery to be kept as small as possible, while nevertheless making available a sufficient quantity of pressure fluid in every situation. These means are combined with the separating valve and the regulating valve, if desired.